Liquid-based Solid Imaging is a process whereby a photoformable liquid is coated into a thin layer upon a surface and exposed imagewise to actinic radiation, for example UV directed by laser for StereoLithography, such that the liquid solidifies imagewise. Subsequently, new thin layers of photoformable liquids are coated onto previous layers of liquid or previously solidified sections. The new layers are then exposed imagewise in order to solidify portions imagewise and in order to induce adhesion between portions of the new hardened region and portions of the previously hardened region. Each imagewise exposure is of a shape that relates to a pertinent cross-section of a photohardened object such that when all the layers have been coated and all the exposures have been completed, an integral photohardened object can be removed from the surrounding liquid composition. In some applications, it is beneficial to view the partially completed article under the liquid resin surface during the building of the article to allow for the determination of whether to abort the build or modify the building parameters on subsequent layers or future builds.
One of the most important advantages of the solid imaging process is the ability to rapidly produce actual articles that have been designed by computer aided design. A significant amount of progress has been made with compositions and processes that have been adapted to improve the accuracy of the articles produced. Also, composition developers have made significant progress toward improving individual properties such as the modulus or Heat Deflection Temperature (also called HDT being the temperature at which a sample of material deforms under a specified load) of the photohardened articles. Typically, a material with a higher HDT will perform better, that is, resist distortion better, in high-heat situations.
However, attempts to simulate a particular set of physical properties of a common manufacturing material to such a degree that the finished article could be easily mistaken for the manufacturing material, based upon look and feel properties, have been limited. For example, U.S. Pat. Nos. 6,287,748 and 6,762,002 describe photocurable compositions used to produce articles having the look and feel of polyethylene and polypropylene articles.
It would be desirable to produce a clear, low viscosity photocurable composition which, upon cure in a stereolithography process, produces an opaque article having the look and feel of the manufacturing material acrylonitrile-butadiene-styrene (“ABS”).
It is known to put various materials in the UV curable resins in order to achieve an opaque article. For example, U.S. Pat. No. 4,942,060 describes use of phase separation in acrylic resins in a process to control depth of curing.
Especially important for the laser based stereolithography process are formulations based on epoxy-acrylic resin mixtures. These formulations further require tougheners to produced balanced mechanical properties. For example U.S. Pat. No. 5,476,748, and subsequent art with such specialised epoxy-acrylic hybrid compositions, disclose use of at least one hydroxy containing ‘toughener’ from either a hydroxy polyester, polyether or polyurethane. There is no mention of using those tougheners which are phase separated to yield toughened, higher HDT compositions.
WO 2005/045523 describes clear resins compositions which on curing give high HDT cured articles. The emphasis is especially regarding non-hydroxy containing acrylic component which is compatible with the epoxy content and the cured resin is a clear polymer.
US 2005/072519 describes certain epoxy-acrylic resins which give stable tensile properties. This involves hybrid compositions without glycidyl epoxy compound.
US 2003/198824 describes epoxy-acrylic resins containing pre-formed reactive particles which provide toughness in the cured resin. Reactive particles containing polysiloxane are described, used in low concentration, to especially yield ABS like properties and glossy cured surfaces.
U.S. Pat. No. 5,972,563 concerns epoxy-acrylic hybrid systems with various hydroxy containing compounds, specifically aromatic compounds with hydroxy groups. The emphasis is to achieve water resistance in the cured resin.
U.S. Pat. No. 5,476,748 sets requirements for accuracy and mechanical properties. There is no mention of using tougheners which are phase separated to yield toughened, higher HDT compositions. Examples show polyester diol containing examples.
In previous art, there is no specific mention of examples of mixed polyols in epoxy-acrylic hybrids which allow differential & preferential separation of toughening microphase domains. These types of clear compositions which go opague are important as low viscosity, needed in operation of the equipment, for example an SL machine, can be achieved, yet yield desired high toughness. Pre-formed tougheners usually cannot be loaded up in effective amounts due to increases in viscosity.